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MongoDB中的聚合

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{
    "_id": ObjectId("512eef329d5d0c9415000025"),
        "tx": {
         "0": "A1",
         "1": "A2",
         "2": "A3"
        },
    "time": NumberInt(1304200205)
} 

{
    "_id": ObjectId("512eef329d5d0c9415000026"),
        "tx": {
         "0": "A4",
         "1": "A5",
         "2": "A6"
        },
    "time": NumberInt(1304200395)
} 

{
    "_id": ObjectId("512eef329d5d0c9415000027"),
        "tx": {
         "0": "A7",
         "1": "A8",
         "2": "A9"
        },
    "time": NumberInt(1304202305)
} 

db.blocks.aggregate(
    {'$unwind':'$tx'},
    {'$group' : { '_id' : {
        'year': {'$year':'$time'},
        'month': {'$year':'$time'},
        },
        'count' : {'$sum':1}            
    }
});

{
    "errmsg" : "exception: can't convert from BSON type NumberInt32 to Date",
    "code" : 16006,
    "ok" : 0
}

这意味着时间字段不是Mongo Date格式，而是NumberInt32。

如何使用聚合函数将其转换为MongoDate。我不想更改数据，因为它来自不同的来源，我每小时导入一次。目前DB中有大约2,000,000条记录正在增加......

问题在约1个月前提出Aggregation Framework - Converting Unix Timestamp to ISODate。如果有人有答案，请在这里发帖...

MongoDB聚合将NumberInt32转换为ISODate

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